One form of sprung seat frame, for example for a vehicle seat, as disclosed for example in U.S. Pat. No. 2,641,307, has a base element, which for example can be fixed to a vehicle floor structure, a top element which forms the upper component of the seat frame structure, and a spring arrangement which is operatively disposed between the base element and the top element. The spring arrangement comprises in superposed relationship at least two leaf springs which are disposed at a spacing from each other and which are at least approximately parallel to each other. The leaf springs are fixed with their one end portion to the base element while the second end portion thereof is fixed to the top element. In the non-loaded condition of the seat frame the leaf springs extend obliquely inclinedly between the base and top elements. The seat frame structure also includes coil springs which connect the end portions of the leaf springs, which are remote from the base element, to each other and to the top element on which the seating member of the seat in which the seat frame is used is disposed. A further coil spring is provided at a central portion between the leaf springs.
It will be seen therefore that this seat frame structure involves a considerable number of individual components, and that has an effect on the assembly and installation particularities of the seat frame. Furthermore that seat frame has only a single precisely defined springing characteristic which cannot be adjusted according to user requirements.
In another form of sprung seat frame or sprung seat which is intended more specifically for a tractor or traction engine, as is found in DE-C-837 965, a lower leaf spring forming part of a spring arrangement disposed between the base element and the top element of the seat frame structure is composed of two leaf spring portions, wherein one leaf spring portion is fixedly connected to the upper leaf spring of the spring arrangement and the second leaf spring portion is of a corrugated configuration and bears movably against the upper leaf spring. That seat frame provides a given constant springing characteristic in dependence on the choice and dimensioning of the spaced-apart leaf springs which are thus disposed one above the other.
Another form of sprung seat having two curved leaf springs which are disposed in side-by-side relationship, as is to be found in FR-A-768 496, also has a given constant springing characteristic. However manufacture of the leaf springs of that seat and more specifically the shaping thereof involves a not inconsiderable amount of work and the aspect of reproducibility also gives rise to problems with the leaf springs of the configuration used therein.
A vehicle seat as disclosed in DE-U-1 794 562 has spring elements which are formed in particular by rubber elements. The rubber elements can be disposed between the seat and strip elements which are angled in a Z-shape and which can also be of a resilient nature. That design configuration also provides a specific constant springing characteristic, as is also the case with a seat frame as disclosed in FR-A-33 758, which is of a very simple design structure.
A similar kind of seat frame in which a spring arrangement comprises two leaf springs disposed at a spacing from each other in side-by-side relationship between the base element of the seat frame and a top element thereof is to be found in DE-C-672 258. The same considerations as set forth in relation to the above-discussed seat frames also apply in regard to the springing characteristic of this seat frame.